Add Family Tree tutorial to demonstrate integration into an application's existing data model

[MarkNahabedian]

This pull request adds the tutorial "Family Tree", which demonstrates how MetaGraphsNext.jl can be incorporated into an application's existing data model to provide graph capabilities.

It also modifies the "test" workflow so that it can be manually triggered.

Currently, this test

    @testset verbose = false "Code formatting (JuliaFormatter.jl)" begin
        @test format(MetaGraphsNext; verbose=false, overwrite=false)
    end

is commented out of test/runtests.jl because it was failing in a fresh clone.

Including the actual family tree data in the tutorial feels like obfuscatory clutter. It's not obvious given how the test/doc examples are structured how to include an auviliarry data file. Suggestions?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cf77b53) 93.46% compared to head (f5f116e) 93.46%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #75   +/-   ##
=======================================
  Coverage   93.46%   93.46%           
=======================================
  Files           7        7           
  Lines         306      306           
=======================================
  Hits          286      286           
  Misses         20       20           

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[gdalle]

Thank you for the contribution! I'm going on holiday now but I'll try to review it in early January :)